The present invention relates to a multistage turbocompressor which, when in operation, conveys a medium from an inlet pressure to an outlet pressure, including, in each case, a plurality of guide-blade cascades and moving-blade cascades which are arranged alternately in the conveying direction, in such a way that, in each case, a moving-blade cascade forms, with a guide-blade cascade following it in the conveying direction, a compressor stage, the moving-blade cascades being arranged on a rotor and the guide-blade cascades on a stator, said turbocompressor having at least one tapping point for at least one further pressure which is between the inlet pressure and the outlet pressure, at which tapping point a part stream of a partly compressed medium is extracted, to a extracted. The invention also relates method for operating a turbocompressor.
A highly efficient method for regulating turbocompressors involves adjusting the guide-blade cascade of one or more stages (Dubbel, Taschenbuch fur den Maschinenbau [Mechanical Engineering Manual], 14th edition 1981 pp 877; Traupel, Thermische Turbomaschinen [Thermal Turbomachines], 3rd Ed. 1982, Vol. 2, pp 111). This regulating method has been employed for a long time, particularly in the case of machines which have to cover a large rotational speed range: in aircraft engines, it is perfectly possible for half the compressor stages to be equipped with adjustable guide-blade cascades. Even with regard to stationary gas turbines of the latest generation, development tends toward designing a plurality of compressor stages with adjustable geometry, as described, for example, in ABB Technology 2/1994, pp 4.
Multistage turbocompressors, precisely those used in gas turbines, have tapping points for extracting compressor air at one or more pressures, the tapping pressure being between the inlet pressure and the outlet pressure. The auxiliary air required at the tapping points is usually needed at a very high pressure level, for example in order to cool the turbine components. The tapping points are therefore mostly located in the rear stages of a compressor. The tapping pressure is thus predetermined essentially by the compressor operating pressure. On the one hand, it is invariable in the case of a specific compressor outlet pressure, and, on the other hand, it varies directly with the operating point of the compressor.
With the turbocompressors customary at the present time and the methods for operating them, it is therefore not possible to provide a defined tapping pressure, irrespective of the operating point of the turbocompressor.
The invention, then, intends to remedy this. The object of the invention, therefore, in a multistage turbocompressor which, when in operation, conveys a medium from an inlet pressure to an outlet pressure, including, in each case, a plurality of guide-blade cascades and moving-blade cascades which are arranged alternately in the conveying direction, in such a way that, in each case, a moving-blade cascade forms, with a guide-blade cascade following it in the conveying direction, a compressor stage, the moving-blade cascades being arranged on a rotor and the guide-blade cascades in a stator, said turbocompressor having at least one tapping point for at least one further pressure which is between the inlet pressure and the outlet pressure, at which tapping point a part stream of a partly compressed medium is extracted, is to provide a possibility for setting the tapping pressure within a wide range, irrespective of the operating point of the compressor.
This is achieved, according to the invention, in that the guide-blade cascade of the stage located immediately upstream of the tapping point and/or of at least one stage arranged downstream of the tapping point is designed with adjustable geometry.
As mentioned initially, in turbocompressors operating over a relatively wide rotational speed range, for adapting the stage kinematics it is perfectly normal to design a relatively large number of moving-blade cascades so as to be adjustable. Here, however, the adjustment of the row of guide blades in connection with the invention serves for controlling the pressure at a specific point in the compressor, irrespective of the compressor operating point. It is therefore expedient and desirable to use the subject of the invention even in compressors which are provided for operating at a constant rotational speed.
By virtue of this design, it is possible for the compressor to have an operating mode in which the work output of the compressor is shifted into the front or the rear compressor stages as a function of the requirements of the tapping point and of the operating point of the compressor.